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Statistical regression methods in environmental chemistry are of vital importance. Regression techniques provide environmental chemical analysts with the ability to calibrate instruments and model large environmental systems.

The rehardening of surface-softened and surface-etched enamel was investigated in vitro and by intraoral exposure. Surface-softened enamel was obtained by treatment with 0.1 M acetic acid buffer solution (pH = 5.5) for 3 h. Surface-etched enamel was obtained by the acid etch procedure used in clinical situations (37% phosphoric acid gel, 30 s). The enamel lesions were treated in vitro, with calcifying solutions for 8 h or were carried for 48 h in an intraoral appliance. Changes at the enamel surfaces were investigated by surface microhardness measurements. Following the treatment with calcifying solutions a significantly greater indentation length was observed in surface-etched than in surface-softened enamel. No significant difference in indentation length between both types of enamel lesions was observed following intraoral exposure. It was concluded that the initial rate of rehardening between both types of enamel lesions is comparable. At his stage remineralization occurs in microspaces created in the slightly destroyed enamel structures. The influence of the etch pits on the indentation length becomes dominating when remineralization continues. An obliteration of etch pits was observed in enamel samples treated with the calcifying solution with the highest degree of saturation. It was suggested that freshly prepared highly supersaturated calcifying solutions can be used to enhance mineral appositions in accidental etch pits.

The load dependency of hardness measurements was investigated on sound and demineralized enamel samples. For all samples investigated, the Knoop hardness number (KHN) varied as a function of the applied load. Higher loads enhanced indenter penetration into the test surface. The variation in KHN values observed in demineralized enamel, both surface-softened and surface-etched, was explained by a decrease in porosity as a function of depth. The reading error for indentations made on surface enamel etched with 37% phosphoric acid gel for 30 s was found to be slightly elevated compared to indentations made on a polished sound enamel surface. It was concluded that the surface microhardness technique can be used for the longitudinal investigation of etched surface enamel.

The in-vitro and in-vivo fluoride release of bioadhesive, slow-release tablets prepared from a mixture of polyethylene glycol polymers, containing 0·1 mg of fluoride as NaF was studied, and their ability to sustain fluoride levels in saliva were compared with conventional fluoride tablets with the same fluoride content. In-vitro release experiments showed that the bioadhesive tablets needed 8 h to release all their fluoride compared with < 1 h for the conventional fluoride tablets. In-vivo, the bioadhesive tablets had a retention period of 6 h and could sustain a salivary fluoride level of more than 10 μm above the baseline for 7 h. The conventional fluoride tablets achieved a peak concentration of 0·5 Mm directly after dissolution in the mouth, but the fluoride level could not be sustained for longer than 1 h. A good agreement was found between the in-vitro swelling behaviour of the bioadhesive tablets and their in-vitro and in-vivo release characteristics and their in-vivo retention time.

The application and the analytical aspects of an acid etch microbiopsy method for the in vitro and in vivo determination of trace elements in the surface enamel of human teeth were reassessed. The method, based on the use of 1.6 N hydrochloric acid in 70% glycerol as the etching agent, provided adequate material for trace element analysis. Optimal standardization of the method required the selection of one tooth type and the analysis of calcium and phosphorus in the etching solutions. In order to reach an acceptable level of reproducibility for the in vivo biopsy method, the etch depths should not exceed 4.5-mu-m. Moreover, the reproducibility of the biopsy was increased by increasing the sampling area.

The bioadhesive characteristics of tablets for oral use made from modified starch, polyacrylic acid (PAA), polyethylene glycol (PEG) and sodium carboxymethylcellulose (CMC) were investigated. Adhesion force and energy were determined in-vitro and maximal adhesion time was evaluated in-vivo in human subjects. In-vitro, PAA showed the best bioadhesive properties, followed by modified maize starch and PEG with a mol. wt of 300 000–400 000 daltons. The presence of 0·1 mg of fluoride as NaF did not lead to significant differences in adhesion force and energy for the same formulation. The in-vivo bioadhesion was not strongly correlated to the in-vitro data. PAA, despite its excellent adhesion, proved to be irritating to the mucosa. PEG with a mol. wt of 200000 daltons was subject to erosion. CMC showed good bioadhesive properties but the mechanical strength of the tablets was low. Modified maize starch tablets containing 5% (w/w) PAA and PEG with a mol. wt of 300 000 daltons proved to be the most suitable formulations for a fluoride-slow-release tablet with bioadhesive properties. In-vitro, the tablets released all of the fluoride within the 8 h period, with a high initial release. The release rate was related to the water absorption rate of the tablets. The PAA-containing formulations and the CMC formulations had the fastest release. In-vivo, fluoride levels with a minimum of 150 and a maximum of 1000 μg mL−1 were maintained for 8 h in the oral cavity. These fluoride levels were sustained significantly longer than those obtained with the administration of fourfold the amount of fluoride in the form of a fluoride-containing toothpaste. The release characteristics in-vivo exhibited a high variation. The use of bioadhesive polymers in oral pharmacotherapy seems promising.

Acid etch surface enamel microbiopsies were taken in vitro and in vivo and analyzed for lead using electrothermal atomic absorption spectrometry. The in vitro samples were obtained from subjects resident in an urbanized region in Belgium or from a region close to a nonferrometal industrial plant. The smaller set of in vivo samples were all from subjects resident in an urbanized region. Using a regression tree approach it was possible to identify in a stepwise manner factors that contributed to the variation of lead in the samples. For the in vitro as well as in vivo samples, the etch depth, tooth type, and age of the subjects were identified as significant factors but sex and dental arch quadrant were not. The residual lead levels obtained after regression with the significant factors were better distributed with much lesser variance. Moreover, a significant higher lead concentration could be demonstrated in the in vitro samples from the region close to the nonferrometal industrial plant.

The influence of fluoride and lanthanum on enamel softening was compared by hardness measurements and by determination of the calcium content in the solution. The addition of lanthanum to an acetate buffer solution (0.05 mollL, pH=5.0) had no significant influence on the change of the indentation length and on the calcium release, compared with those of the control group. In the fluoride group, a moderate increase of the indentation length and a reduced calcium loss were observed. In a second experiment, surface-softened bovine enamel was treated with calcifying solutions (Ca/P ratio = 1. 67). Differences in treatment were created by the addition of traces (2 ppm) of lanthanum, fluoride, or both. The acid resistance of the treated enamel was evaluated by two successive softening steps (0.1 mol/L acetate buffer, pH = 5.5). Alterations of the enamel surface were longitudinally followed with a hardness tester. The addition of fluoride, lanthanum, or both significantly improved the rehardening of surface-softened enamel, compared with that of the control group. A 2 x 2 factorial analysis of variance showed that lanthanum and fluoride had a highly significant main effect and a significant negative interaction effect on the rehardening of surface-softened enamel. Subsequent acid treatments revealed that only samples treated with a fluoride-containing solution were adequately protected from further dissolution. The enamel surfaces treated with a solution containing both lanthanum and fluoride were covered with an acid-resistant surface coating. SEM observation of this surface layer revealed the presence of globular and spherulite structures.

The major element and trace metal analytical results of a strong acid digestion have been used to model natural and enhanced trace metal concentrations in surface sediment samples from Cleveland Bay. The natural ranges in concentration of cadmium, cobalt, copper, nickel, lead and zinc in sediments have been modelled by multiple linear regression using major elements as independent variables. Sites that exceed the upper 95% prediction interval of the regression model of the natural range in concentration are classified as enhanced. Enhancement of sites by metals derived from anthropogenic sources is characterized by enhancement of cadmium, copper, lead or zinc, and can be identified by Principle Components Analysis. Sites that contain metals derived from anthropogenic sources occur within the intertidal and near-shore sediments of western Cleveland Bay. No evidence of trace metals derived from anthropogenic sources was found within the sediments of the central bay.

An implementation of the k NN classification method of Loftsgaarden and Quesenberry is discussed. It is a theoretically valid alternative for probabilistic pattern recognition by means of the Bayes equation. The method is illustrated on the basis of a data set containing laboratory tests for three categories of functional states of the thyroid gland and the performance is compared with those of other probabilistic pattern recognition techniques. Although the results are acceptable, the k NN method did not perform as well as some other probabilistic techniques.

In this in vitro study the influence of viscosity and surface tension of dental fluoride-containing gels, morphological characteristics of human and artificial occlusal fissures and the penetration of these fluoride gels into fissures is demonstrated. Self-prepared hydroxyethylcellulose gels with viscosities ranging from 75 to 5800 mPas containing 1.23% NaF are used. Sodium laurylsulphate was added to one group. While viscosity plays a secondary role in the penetration of the gels, surface tension and fissure morphology are very important. The shallow-wide type of fissure is filled by all of the gels. The deep-narrow type of fissure is penetrated only by gels containing sodium laurylsulphate.

The effectiveness of five in-vitro laboratory tests for differentiation between three thyroid functional states (EU, HYPO and HYPER thyroidism) has been determined by using statistical linear discriminant analysis. The optimal linear combination of laboratory tests obtained by means of linear discriminant analysis results in a better use of the information present in each test, so that the possible redundancy of tests can be assessed. In this context, some feature selection criteria were evaluated. It is shown that in this application only two laboratory tests are necessary to obtain a sufficiently high diagnostic effectiveness when linear discriminant analysis is applied.

Second upper molars from 3-day-old rats were cultured by the Trowell method for 14 days. One of each pair of molars was kept as an uncultured control; the other was cultured. Explants were exposed to eight different combinations of Ca, Mg and P additions to BGJb medium. This resulted in eight groups of explants (control, Ca, Mg, P, CaMg, CaP, PMg and CaMgP) and their eight uncultured contralateral groups. The additions were calculated to double the original measured media concentration. Cultured and uncultured germs were analysed for dry weight (D), ash weight (A), Ca, Mg and P content. The organic fraction (D — A) was calculated. The analysis of covariance by means of multiple regression revealed that Ca-addition to the culture medium stimulated D, A, Ca and P in the explants; P-addition was stimulatory for D, A, D — A and P whereas Mg addition was inhibitory for A, D — A and Ca. A positive interaction for all the tooth-germ variables was demonstrated after CaMg addition; an antagonistic effect was found for the tooth-germ variables D, A, Ca and P after CaP addition. The value of the tooth-germ variables at the time of explantation (covariate) had no significant effect on the value for the variables of the explants (except on their P content). The highest absolute values for all the variables were obtained after CaMg and CaMgP additions. Furthermore, taking into consideration morphological results, the addition of CaMgP can be recommended as medium supplement in the organ culture of rat tooth germs.

The first step in multivariate analysis is almost always the scaling of the variables. The pattern recognition technique SIMCA provides the possibility of scaling the variables over all the objects of the training set (classical scaling), or only over the objects belonging to the same group (separate scaling). The former method of scaling is the more used. The effect of separate scaling on the classification of objects with SIMCA is investigated for a data set consisting of the percentage distribution of fatty acids in olive oils originating from two neighbouring regions in Italy. It is shown that separate scaling has a beneficial effect on the classification.

Principal components analysis (PCA) was used for the investigation of an air pollutants data base. The data set consists of nearly 400 measurements of 26 gaseous organic compounds and meteorological data. The measurements were carried out at four different places in The Netherlands. PCA is a simple way to display visually most of the total variation in a few dimensions. It is helpful in the identification of outliers, the recognition of sources and the investigation of meteorological effects.

It is shown that ALLOC when associated with descriptive statistical linear discriminant analysis (“display” SLDA) is in some situations a better alternative than ALLOC and SLDA for classification purposes (“classification” SLDA). It is possible with a combination of “display” SLDA and ALLOC to adjust the suboptimal decision boundaries of “classification” SLDA when the underlying assumptions about the data in “classification” SLDA are not fulfilled, whereas the combination of “display” SLDA with ALLOC permits classification of new objects without computer assistance which is not possible with ALLOC alone. The performance of “display” SLDA—ALLOC is discussed on the basis of the differentiations between THYROID functional states.

The use of multivariate confidence regions is proposed for the classification of clinical laboratory profiles into diagnostic classes. For this purpose, a multivariate confidence region is developed for each diagnostic class. Three methods (UNEQ, EQ, and SIMCA) are evaluated and compared with classical linear discriminant analysis. As an example, a small data set concerning the differentiation of the thyroid functional states on the basis of five laboratory tests is used. It is shown that related procedures can produce results of very different quality and that the multivariate region approach is attractive for the clinician's daily practice since the methods are easily implemented on a microcomputer.

Osteocalcin was localized by indirect immunogold staining of thin frozen sections of rat tooth germs which had been fixed by different methods. Acrolein fixation proved to be satisfactory considering the preservation of fine structure and antigenicity. In odontoblasts, osteocalcin was found to be localized in the cisternae of the rough endoplasmic reticulum and Golgi apparatus. Few positive transport vesicles were found. Staining for osteocalcin in odontoblastic processes was only observed after strong fixation and was intense in odontoblasts engaged in early dentine formation. Predentine was slightly positive in the neighbourhood of positive processes. Matrix vesicles were negative and strong osteocalcin labeling of dentine seemed to appear after the onset of mineralization.

The feature selection procedure of ALLOC is compared with the SELECT procedure in the ARTHUR software package and with a procedure based on statistical tests in the SPSS software package. Since ALLOC classification is very sensitive to redundant variables, feature selection is necessary. This is not a disadvantage because detection of redundant variables is always desirable. The ALLOC selection procedure performs very well in the two applications considered here, i.e., differentiation of milk samples and characterization of thyroid function.

Osteocalcin was purified by gel chromatography from a crude extract obtained after decalcification of rat incisors. The apparent molecular weight, as determined by 5-15% SDS-polyacrylamide gel electrophoresis, was 18,000, and amino acid analysis revealed 60 γ-carboxyglutamic acid residues per 1000. Antisera against osteocalcin, raised in rabbits, reacted specifically with osteocalcin when investigated by immuno-electroblotting of dentin crude extract. 4-μm cryosections of formaldehyde-fixed tooth germs showed positive immunocytochemical staining for osteocalcin in dentin and odontoblasts. The staining of the mantle dentin at the coronal sides of the tooth germs was more intense than that of the adjacent circumpulpal dentin, while the odontoblasts involved in the formation of mantle dentin showed stronger immunoreactivity than did odontoblasts involved in circumpulpal dentin formation. This marked difference was not observed on the root sides of the tooth germs. In 1-μm cryosections, osteocalcin immunoreactivity was found evenly distributed throughout the entire cell body, with the exception of the Golgi region, which was less intensely stained, while the nucleus and the cell process were negative. The positive staining reaction with anti-osteocalcin antiserum was found in dentin from the very onset of its formation in the fetus. ln conclusion, our results demonstrate the presence of osteocalcin in odontoblasts and dentin. Its immunocytochemical localization may be compatible with a distinct role in early dentinogenesis.

Second upper molars from 3-day postnatal rats were cultured for 2 weeks and compared with in-vivo specimens from 7-day postnatal rats. Several preparatory techniques were applied to expose the extracellular matrices, the three-dimensional structure of which were examined by SEM. The combination of phosphate-buffered saline and ultrasonics as preparation for the observation of the enamel, hypochlorite treatment to study the predentine, the freeze-fracture technique for the dentinal tubules and oxygen-plasma-ashing for the mineralization front of dentine gave best results. Enamel formed in vitro was prismatic similar to in vivo. The fissures were devoid of enamel and the enamel-free areas at the cusp tips were larger than in vivo. In the cervical area in vitro, the enamel stopped abruptly instead of gradually decreasing. The predentine and the dentine were normal in structure.

In this paper sixteen discrimination techniques are compared on the basis of a data base concerning the thyroid function. Five laboratory tests are available for 215 patients divided into three diagnostic classes, i. e. euthyroidism, hypothyroidism and hyperthyroidism. For all techniques correct classification rates were determined using the leave-one-out procedure. Moreover, for the probabilistic techniques, the quality of the obtained probabilities was evaluated. It has been shown that most of the techniques perform well. However, the probabilistic techniques are to be preferred.

Different alternatives for the determination of tannins in tea with Cu ionspecific electrodes and atomic absorption spectrometry are discussed. The methods are based on the precipitation of tannins with copper acetate. A screening of methods is carried out in three successive steps: determination of (1) Cu in a simple aqueous solution, (2) tannic acid in aqueous solution and (3) tannins in tea. Two procedures are proposed as suitable tools for tannin determination in tea, i.e. direct potentiometry of excess Cu2+ and AAS, the first being the easiest and most rapid.

Belgium is among the European countries that are the most affected by allergic rhinitis. Pollen grains and fungal spores represent important triggers of symptoms. However, few studies have investigated their real link with disease morbidity over several years. Based on aeroallergen counts and health insurance datasets, the relationship between daily changes in pollen, fungal spore concentrations and daily changes in reimbursable systemic antihistamine sales has been investigated between 2005 and 2011 in the Brussels-Capital Region. A Generalized Linear Model was used and adjusted for air pollution, meteorological conditions, flu, seasonal component and day of the week. We observed an augmentation in drug sales despite no significant increase in allergen levels in the long term. The relative risk of buying allergy medications associated with an interquartile augmentation in pollen distributions increased significantly for Poaceae, Betula, Carpinus, Fraxinus and Quercus. Poaceae affected the widest age group and led to the highest increase of risk which reached 1.13 (95% CI [1.11-1.14]) among the 19- to 39-year-old men. Betula showed the second most consistent relationship across age groups. Clear identification of the provoking agents may improve disease management by customizing prevention programmes. This work also opens several research perspectives related to impact of climate modification or subpopulation sensitivity.

The effect of addition of eight different combinations of Ca, Mg and P supplements (control, Ca, Mg, P, CaMg, CaP, PMg and CaMgP) on three-day-old rat maxillary second molars, explanted at the premineralizing stage and cultured for two weeks, was studied. Light-microscopy sections, cut parallel to the occlusal plane, were divided into four sectors and given a score according to an ordinal scale for dentine and enamel depending on the regularity of these matrices. An analysis of variance on these scores revealed a significant favourable effect of Mg, CaMg and CaMgP and an adverse effect of Ca on enamel. A favourable effect on dentine regularity was obtained after addition of Ca or Mg. Ultrastructurally, enamel changes such as amorphous enamel matrix, voids and disturbance in rod-interrod pattern were seen after addition of Ca, P, CaP. Thin enamel with less tight packing of crystals was observed after CaMg addition. A thick layer of enamel with highly-organized rod-interrod pattern was seen with Mg, PMg and CaMgP addition. It is suggested that Mg plays an important role in the interaction with Ca and P for the harmonious development of enamel and dentine in vitro.

In this in vitro study the ability and speed of self-gelling liquid compositions to penetrate into fissures were evaluated. Two formulations containing either tetraethylsilicate, ammonium fluoride, and sodium lauryl sulfate or tetraethylsilicate, sodium fluoride, and cetylpyridinium chloride at different concentrations were used. It is shown that fissure penetration occurs when a certain minimum content of surface-active agent is present. Fissure penetration is achieved within 3-4 s, according to the fissure morphology.

Trace elements can influence dental health, possibly by altering tooth resistance during preeruptive development. Therefore, it was investigated whether lead and fluoride would be incorporated into the calcifying matrices or the cellular parts of tooth germs in vitro. Using laser microprobe mass analysis, the localization of lead and fluoride was studied in the different layers or tooth germs that had been cultured in a medium to which PbCl2 of NaF had been added in different concentrations. Both elements could only be detected in the dentine layer. Hence, the enamel organ in the secretory stage of tooth development excludes lead and fluoride from the enamel, even when enamel formation by the ameloblasts is visibly disturbed. Furthermore, there seemed to be a process of saturation in the accumulation of lead and fluoride in the dentine.

We performed a retrospective study on 163 subjects suffering from rheumatic fever (16), rheumatoid arthritis (36), lupus erythematosus (17), gout (21), arthrosis (50) and osteomyelitis (23). The number of variables evaluated was 39. These were all of a general biochemical and haematological nature. A feature reduction resulted in sixteen variables that matched well with those known from the literature. Linear discriminant analysis yielded poor results in classifying the six disease categories (with 18 variables 61.8%). A reduction to three disease categories improved the classification results remarkably. This, and the excellent discriminating power between patients and the reference group, shows that the selected variables are illustrative only for general clinical pictures, such as infection, and not for the desired differential diagnosis.

SummaryThe differential diagnosis between multiple myeloma and benign monoclonal gammopathy has been investigated on the basis of a statistical model incorporating simultaneously four parameters, which refer to the cellular monoclonal event. The combination of the amount of bone marrow plasma cells, their monoclonal fraction and the concentration of the monoclonal immunoglobulin in the serum has been proven to give an optimal classification of patients with multiple myeloma and benign monoclonal gammopathy. Symptom free patients belonging to this group, are of special interest for the clinical follow-up, as they present an initial high monoclonal plasma cell mass.

Antisera against bovine and rat osteocalcin were characterized and used for the immunocytochemical visualization of this protein in human and bovine teeth. Osteocalcin immunoreactivity was localized at the dentino-enamel junctions, whereas the major part of the dentin was unstained. These results suggest some involvement of ameloblasts in the deposition of osteocalcin. The low concentration of the protein suggests that it has no direct function in dentin formation.

The intrathyroidal stable iodine (ITI) determined in 776 patients chosen at random. Ninety % of these patients presented with nontoxic goiter. Curve-filtering analysis techniques showed a seasonal variation in ITI: an acrophase was found in April/May, a nadir in September/October. The possible relationship of this seasonal variation with the intake of iodine or alimentary antithyroid substances are discussed, as well as possible relationship with variation in chronic TSH stimulation related to ambient temperature.

A retrospective study was performed on 186 subjects suffering from rheumatic fever, rheumatoid arthritis, lupus erythematosus, gout, arthrosis, osteomyelitis and a group of patients with negative rheuma-serology test results but positive joint complaints. The aim was to examine by means of selected variables the group with negative rheuma-serology test results and positive joint complaints. In order to see if these patients were distinct from the other disease categories or were ’precursor’ to one of these disease states. The statistical methods used were: stepwise linear discriminant analysis, k-nearest neighbour method, linear learning machine, hierarchical clustering and principal component analysis.

Discriminant analysis is used to identify different milk samples on the basis of the gas chromatographic data for fatty acids in 20 samples each of milk fat from cows, sheep, and goats. The method can differentiate mixtures and pure milks with a high degree of correct classifications. A good discrimination can also be obtained by using a reduced set of variables. The method is useful for the interpretation of gas chromatographic data and should allow a higher proportion of correct classifications than is possible by visual inspection of the chromatograms.

PURPOSE: To study the frequency of and factors associated with the decision to perform single implant treatment after tooth extraction by general practitioners in a private, fee-for-service setting. MATERIAL AND METHODS: One hundred practitioners with a general dental practice in Ghent were randomly selected. Clinicians were asked to fill in a study form for every single extraction they performed during an 8-week period. The form related to the treatment decision and a number of patient- and clinician-related factors. RESULTS: Ninety-four general dentists (52 men, 42 women; mean age 49; range 24-68) agreed to participate and extracted 1180 single teeth. After exclusion of third molars and cases where the reason for tooth loss would generally prohibit replacement, 900 cases were identified. In 24% of these patients, there was no treatment decision and in 18% replacement was deemed unnecessary. When replacement was necessary (n = 526), removable partial denture (RPD), fixed partial denture (FPD), single implant treatment and resin-bonded bridge were chosen in 54%, 24%, 21% and 1% of the patients, respectively. Multinomial logistic regression was used to evaluate the decision-making process for single implant treatment against RPD and FPD. In relation to RPD, single implant treatment was more likely in highly educated patients with few missing teeth and no bone loss at adjacent teeth. In relation to FPD, single implant treatment was more likely in patients with intact adjacent teeth and when the tooth was extracted by a female dentist. Experience in implant prosthetics was positively associated with single implant treatment in all analyses. CONCLUSIONS: Single implant treatment is not the most common procedure in daily practice to restore a single tooth gap. Patient's education, oral factors and clinician-related factors may affect the decision-making process, whereas medical factors may not.

In order to select chromatographic starting conditions to be optimized during further method development of the separation of a given mixture, so-called generic orthogonal chromatographic systems could be explored in parallel. In this paper the use of univariate and multivariate regression trees (MRT) was studied to define the most orthogonal subset from a given set of chromatographic systems. Two data sets were considered, which contain the retention data of 68 structurally diversive drugs on sets of 32 and 38 chromatographic systems, respectively. For both the univariate and multivariate approaches no other data but the measured retention factors are needed to build the decision trees. Since multivariate regression trees are used in an unsupervised way, they are called auto-associative multivariate regression trees (AAMRT). For all decision trees used, a variable importance list of the predictor variables can be derived. It was concluded that based on these ranked lists, both for univariate and multivariate regression trees, a selection of the most orthogonal systems from a given set of systems can be obtained in a user-friendly and fast way.

Acid etch surface enamel microbiopsies were performed on teeth from 378 children aged 6–12 years; 318 of the children lived in Belgium, an industrialized country, and 60 lived in a rural part of Kenya. In addition to lead and cadmium, calcium and phosphorus were also quantitatively determined in the etch solutions. Calcium was chosen as an internal reference for the expression of the lead and cadmium concentrations and for the assessment of the etch depth. The mean lead level in surface enamel of the Belgian children was approximately eight times higher than that of the Kenyan children. The cadmium levels were not significantly higher. An appropriate regression model taking into account differences in etch depth showed that a significant decrease of lead and cadmium with etch depth occurred and that a significant correlation between lead and cadmium in surface enamel existed for the Belgian cohort. Moreover, the same mean calcium/phosphorus ratios were obtained for the Belgian and Kenyan surface enamel samples, and were found not to play a significant role in the calibration of the lead and cadmium levels.

The use of the classification and regression tree (CART) methodology was studied in a quantitative structure–retention relationship (QSRR) context on a data set consisting of the retentions of 83 structurally diverse drugs on a Unisphere PBD column, using isocratic elutions at pH 11.7. The response (dependent variable) in the tree models consisted of the predicted retention factor (log kw) of the solutes, while a set of 266 molecular descriptors was used as explanatory variables in the tree building. Molecular descriptors related to the hydrophobicity (log P and Hy) and the size (TPC) of the molecules were selected out of these 266 descriptors in order to describe and predict retention. Besides the above mentioned, CART was also able to select hydrogen-bonding and molecular complexity descriptors. Since these variables are expected from QSRR knowledge, it demonstrates the potential of CART as a methodology to understand retention in chromatographic systems. The potential of CART to predict retention and thus occasionally to select an appropriate system for a given mixture was also evaluated. Reasonably good prediction, i.e. only 9% serious misclassification, was observed. Moreover, some of the misclassifications probably are inherent to the data set applied.

Presents a two-stage classification procedure for the recognition of Thai characters. Two classifiers are used to initially classify the characters into different groups and then to classify the characters within each group. Both a backpropagation multi-layered perceptron and a discriminant analysis technique, called penalised discriminant analysis, are used for classification. A comparative performance analysis of the two classifiers is given. To effectively decorrelate the feature vectors, a wavelet transform is also introduced during the preprocessing phase.

OBJECTIVES: To investigate determinants of medication use among multi-ethnic pregnant women. METHODS: A total of 641 pregnant women participated in this cross-sectional study in a Brussels university hospital. A questionnaire was used to obtain data on socio-demographic characteristics and medication use. Chi-squared tests and binary logistic regression analyses were performed using SPSS 19. RESULTS: Medication use during pregnancy (37%) was positively associated with age older than 35 years, Western origin, being born in Belgium, high education and employment status. Highly educated Western women had a greater exposure to drugs with an unknown safety profile than Arab/Turkish and 'Other (non-Western) origins' women. In the latter two groups, low education and nulliparity were the most important determinants of lower drug use. Nulliparous Arab/Turkish women used significantly less medications (17%) during pregnancy than parous women with the same ethnic background (34%; p = 0.024). CONCLUSIONS: Medication use during pregnancy is considerable but differs according to ethnicity. Age, parity, educational level, occupational status and duration of stay in Belgium are important determinants that should be taken into account for risk assessment and preventive measures targeting pregnant women.

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Sound and surface-softened bovine enamel samples were treated for 24 h with calcifying solutions (Ca/P ratio = 1.67) enriched with fluoride (0.5 or 1 mg/L), lanthanum (1 or 5 mg/L) or both. Lanthanum and fluoride containing calcifying solutions formed coatings on the enamel surfaces. The significant increase in indentation length observed in the sound enamel samples after treatment was related to the presence of the coating. The fluoride content of the acid-etch biopsy material, taken from enamel surfaces after treatment, was increased by the addition of lanthanum to fluoride containing calcifying solutions. This observation was made on both sound and surface-softened enamel samples.

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